Hypothesis: That volunteers who receive the new candidate oral vaccines for enterotoxigenic E. coli, strains PTL002 and PTL003, in doses of 5x10(7), 5x10(9) and 5x10(10) per dose will excrete the vaccine strain in their stool, will have no symptoms related to ingesting the strains, and will develop intestinal antibodies to the E. coli colonization factor antigen, CFA II. These attenuated strains of E. coli produce neither heat labile toxin (LT) nor heat stable toxin (ST) but do express CFA II antigen and they have metabolic defects that limit their growth. It is hoped that when they are given orally, they will stimulate protective anti-CFA immunity.